Enrichment ratio method

The residence time for retinol in the test subject was predicted by the compartmental model to be 474 days. The residence time of 474 days is in excellent agreement with the 460 day MST that can be calculated from the data of Song et al. (1995) using the enrichment ratio method (Cobelli and Saccomani, 1992). Also, an MST of 105 to 337 days can be calculated from the half-life values (75 to 241 days) of body vitamin A reported by Sauber-lich et al. (1974) who depleted human subjects with vitamin A-deficient diets. At the same time the empirical description predicted the MST for retinol to be 26 days. While the reason for such a large discrepancy in MST (474 versus 26 days) between the compartmental model and the empirical description prediction is unclear, it is not likely to be accounted for by slight errors in estimating the final slope of the plasma retinol-d4 decay curve. Because the compartmental model embodies several features of retinol metabolism de novo production and release of retinol can occur in unobservable compartments, etc.) in addition to plasma retinol concentrations, its predicted MST is more likely to better reflect the dynamics of retinol metabolism. 

Feldman et al. (1979a,b) were the first to demonstrate a reduction in cholesterol absorption due to dietary stearic acid in rats. The investigators used three different methods to quantify cholesterol absorption (i.e., plasma isotope ratio method, fecal dual isotope method, and lymph duct can-nulation), and in each case absorption was significantly decreased by stearic acid. Other studies using lymph duct cannulated rats fed stearic acid-enriched diets showed significant reductions in cholesterol absorption (Chen et al., 1989 Ikeda et al., 1994). Using a more realistic dietary approach,... 

To prevent grain boundary segregation, methods based on the conelation of enrichment ratio with the inverse of solid solubility have been used in several cases. Johnson et al., for example, ) proposed doping nickel-based alloys with additives such as hafnium, zirconium or lanthanum in order to remove sulfur from solution by the formation of sulfides during solidification thus preventing segregation and subsequent embrittlement. 

If the distribution equilibrium is not reached in individual stages of the cross-flow cascade, the described method may also be applied to find the actual or practical number of stages Np. An auxiliary line has to be introduced in Fig. 6-14 instead of the equilibrium line, which considers the enrichment ratio for each stage). 

For ail samples, both a.p. and s.o., irrespective of the preparation method, the experimental intensity ratios, V2p/Zr3d, increased proportionally to the V-content up to 3 atoms nm 2 (pjg 2). The ratio approaches those calculated with the spherical model proposed recently by Cimino et al. [27] (full line in Fig. 2). For ZV samples with V-content < 3 atoms nm 2, this finding shows that vanadium species are uniformly spread on the Zr02 surface. On ZV catalysts with a larger V content (not shown in Fig. 2), the intensity ratios were markedly larger than the corresponding values yielded by the spherical model. The results obtained on samples with V-content > 3 atoms nm 2 point therefore to a V surface enrichment. 

Au, Sb and Hg are more enriched into the ores of back-arc basins compared with midoceanic ridge and thus it is likely that back-arc basin hydrothermal flux for these elements is higher than midoceanic ridge hydrothermal flux. However, the concentrations of these elements in back-arc basin hydrothermal solution have not been analyzed. Thus, we need to accumulate analytical data on the concentration of these elements in back-arc basin hydrothermal solution. Further, H2O flux from back-arc basin has to be estimated based on various methods ( He/He, Mg concentration, Li isotope, Sr isotope, Ge/Si ratio) which was argued for midoceanic ridge hydrothermal system by Elderfield and Schultz (1996), but not for back-arc basin by the previous workers. 

Generally, performance of a method is often judged in one of two ways. The first is the enrichment factor, enrichment for short, which is the ratio of the cumulative number of actives in the top N% of the total number in the dataset to random retrieval rate. Many early studies focused on the enrichment obtained when the top 10% of the dataset was screened. However, this is operationally unrealistic if compound collections exceed 100,000 compounds, which is common in mid- to large-sized companies. A more realistic test is the enrichment obtained in the top... 

Isotope dilution mass spectrometry (IDMS) can be applied with most of the ionisation methods used in mass spectrometry to determine isotope ratios with greater or lesser accuracy. For calibration by means of isotope dilution, an exactly known amount of a spike solution, enriched in an isotope of the element(s) to be determined, is added to an exactly known amount of sample. After isotopic equilibration, the isotope ratio for the mixture is determined mass spectrometrically. The attraction of IDMS is its potential simplicity it relies only on the measurement of ratios. The... 

Enrichment of the analyte to improve the signal-to noise-ratio and the detection limit of the analytical method, respectively... 

Further mechanistic work has revealed interesting solvent effects on diastereo-selectivity103. A method for enriching isomer ratios in favor of the trans or exo... 

---